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Written by Larry Gay
The Froliech tractor, built in 1892, has been described as the first tractor to propel itself forwards and backwards and the other early tractors provided one speed forward and one speed in reverse. By the 1920s, farm tractors were featuring two and three forward speeds. As rubber tires became popular in the mid-1930s, a faster road speed was provided which usually added an additional speed to the transmission. Soon some of the tractors were featuring five- and six-speed transmissions.
International Harvester introduced its Torque Amplifier transmission in 1954 which provided a shift-on-the –go slower speed for each of the five gears for a total of 10 forward speeds. Other tractor manufacturers soon introduced their versions of a partial powershift transmission and the Ford Select-O-Speed full powershift transmission was introduced in 1959 with 10 forward speeds. The International 656 tractor was built with a hydrostatic transmission which provided an infinite number of speeds, but the efficiency was poor with heavy drawbar loads.
The AGCO Corporation purchased Xaver Fendt GmbH & Co., the leading German manufacturer of tractors, in 1997 and then introduced the Fendt line of nine models of tractors in North America in 2000. The Fendt tractors featured the Vario transmission which had been introduced in Germany in 1995. This transmission introduced the new concept of a stepless transmission for farm tractors.
The Vario transmission was a continuously variable transmission which used a planetary gear to split the power between hydrostatic and mechanical drives to provide an infinite number of speeds. The power was delivered to the mechanical drive unit by the sun gear and to the hydrostatic unit by the ring gear. Most of the power was transmitted by the hydrostatic section at low speed, but more power was produced by the mechanical section as the speed was increased. There were two speed ranges with the low range providing an infinite number of speeds up to 20 mph and up to 31 mph in the high range.
The Vario transmission was controlled by a joystick on the armrest console. Pushing forward increased the tractor’s speed and pulling back slowed the speed. Reverse was activated by pulling back on the joystick after the tractor was at a standstill. Moving the joystick to the left provided shuttle shifting and to the right engaged cruise control speeds. . The net result was an infinite number of speeds like a hydrostatic transmission, but with better efficiency.
This type of transmission is becoming popular and is now available in AGCO’s Massey Ferguson and Challenger tractors and John Deere, Case IH, and New Holland tractors.
Larry Gay is the author of four tractor books and the "Machinery Milestones" articles in Heritage Iron magazine. To learn more about this magazine which focuses on the 1960-1985 era, go to heritageiron.com or call 1-855-old-iron.
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